Answer:

Step-by-step explanation:
Let
be the average of the sample, and the population mean will be
We know that:
gr
Let
be the standard deviation and n the sample size, then we know that the standard error of the sample is:

Where


In this case we are looking for:

This is:
or 

Now we get the z score



Looking at the tables for the standard nominal distribution we get


Answer:
18
Step-by-step explanation:
There are 2+3 = 5 ratio units representing 45 band members, so each ratio unit represents 45/5 = 9 band members.
The 2 ratio units of sixth graders represent 2×9 = 18 sixth grade band members.
Answer:
ON MONDAY: 35 mosquitos.
ON TUESDAY: 6 flies.
Step-by-step explanation:
As you can see in the diagram, the frog eats 3 flies for every 7 mosquitoes (for lunch). Then you can expresed this ratio as following:
3:7 or 
Based on the table:
-If the frog eats 15 flies on monday, then the number of mosquitos that it eats can be calculated as following:

-If the frog eats 14 mosquitoes on tuesday, then the number of flies that it eats can be calculated as following:

Answer:
Yes, the probability distribution is valid.
Step-by-step explanation:
Given :
Income range ___ midpoint(x) ___ %
5 - 15 __________ 10 _____20%
15 - 25 _________ 20 _____13%
25- 35 _________ 30 _____ 21%
35 - 45 _________40 _____ 17%
45 - 55_________ 40 ____ 20%
55 or more _______ 50 _____9%
Yes, we do have a valid probability distributuon ; as the summation of the percentage values is equal to 100%